The present invention relates to an apparatus for transferring a wafer etc. in a vacuum chamber.
Conventionally, this kind of the transferring apparatus is provided with a tubular partition wall having a rectangular section or a circular section within a vacuum camber. The inside of the partition wall is held under the atmospheric state. On the other hand, the outside of the partition wall is exposed to the vacuum state in the vacumm chamber.
A floating carrier having a feeding rod is arranged around the outer periphery of the partition wall. On the other hand, an actuating block is disposed inside the partition wall. The actuating block is provided with magnetic bearings around its outer periphery, and is constructed to undergo a reciprocal displacement between the opposite ends of the tubular partition wall. The magnetic bearings are comprised of a plurality of electromagnets and a plurality of sensors. Each sensor operates to detect a floating position or a gap of the floating carrier, while each electromagnet is activated according to detected values outputted from the sensors. By such an operation, magnetic force is applied to the floating carrier through the partition wall to support the floating carrier.
In operation of the above described transferring apparatus, after the carrier is provisionally floated and supported by the magnetic bearings, the actuating block is operated to undergo reciprocal displacement. The floating carrier is displaced reciprocally according to the movement of the actuating block so that the feeding rod on the floating carrier effects transfer of the wafers.
However, in the above noted transferring apparatus of the prior art, the tubular partition wall has a rectangular section, hence the partition wall may be deformed due to pressure difference inside and outside the partition wall. Such deformation may be prevented if the thickness of the partition wall is increased. However, in such a case, the increased thickness weakens the magnetic force applied from the electromagnets to the floating carrier through the partition wall. Therefore, it would be necessary to increase an exciting current of the electromagnets, thereby causing drawbacks such as increase in power consumption of the transferring apparatus or device and heat generation from the electromagnets of the device.
On the other hand, another type of the conventional transferring device utilizes a tubular partition wall of a circular section instead of the sectionally rectangular partition wall. The circular partition wall may not develop deformation even if the thickness of the partition wall is decreased. Therefore, the circular partition wall can facilitate reduction in power consumption of the device and can suppress heat generation. However, it is generally difficult to produce a tubular partition wall of the circular section having a small thickness, and a thin tubular partition wall has disadvantageouslly a poor mechanical or structural strength.